Bài `5:`
`a)`
`5x (1/5x -2) + 3(6-1/3x^2) = 12`
`=> x^2 - 10x + 18 - x^2 = 12`
`=> -10x + 18 = 12`
`=> -10x = 12 -18`
`=> -10x = -6`
`=> x = 3/5`
Vậy `x=3/5`
``
`b) 7x (x-2) - 5(x-1) = 7x^2 +3`
`=> 7x^2 - 14x - 5x + 5 = 7x^2 +3`
`=> 7x^2 - 14x - 5x - 7x^2 = 3 - 5`
`=> -19x = -2`
`=> x = 2/19`
Vậy `x = 2/19`
``
`c) 2(5x-8) - 3(4x-5) = 4(3x-4) +11`
`=> 10x -16 - 12x + 15 = 12x - 16 + 11`
`=> 10x - 12x - 12x = -16 + 11 + 16 - 15`
`=> -14x = -4`
`=> x= 2/7`
Vậy `x=2/7`
``
`d) 5x - 3 {4x - 2 [ 4x - 3 (5x-2)]} = 182`
`=> 5x - 3 [4x - 2 (4x - 15x + 6)] = 182`
`=> 5x - 3 (4x - 8x + 30x - 12) = 182`
`=> 5x - 12x + 24x - 90x + 36 = 182`
`=> 5x - 12x + 24x - 90x = 182 - 36`
`=> -73x = 146`
`=> x = -2`
Vậy `x=-2`
``
`A= x (2x+1) - x^2 (x+2) + (x^3 - x +3)`
` = 2x^2 + x - x^3 - 2x^2 + x^3 - x + 3`
` = (x^3 - x^3) + (2x^2 - 2x^2) + (x-x) + 3`
` = 0 + 0 + 0 + 3`
` = 3`
